102,934 research outputs found
Magnetic Reconnection in Turbulent Plasmas and Gamma Ray Bursts
We discuss how the model of magnetic reconnection in the presence of
turbulence proposed inLazarian & Vishniac 1999 makes the reconnection rate
independent either of resistivity or microscopic plasma effects, but determined
entirely by the magnetic field line wandering induced by turbulence. We explain
that the model accounts for both fast and slow regimes of reconnection and that
this property naturally induces flares of reconnection in low beta plasma
environments. In addition, we show that the model involves volume reconnection
which can convert a substantial part of the energy into energetic particles. It
is important that the reconnection induces an efficient acceleration of the
first order Fermi type. Finally, we relate the properties of the reconnection
with the observed properties of gamma ray bursts and provide evidence
supporting the explanation of gamma ray bursts based on energy release via
reconnection.Comment: 12 pages, review talk at 5th International Symposium on High-Energy
Gamma-Ray Astrophysics, Heidelber
Cosmic Ray transport in MHD turbulence: large and small scale interactions
Cosmic ray (CR) transport and acceleration is essential for many
astrophysical problems, e.g., CMB foreground, ionization of molecular clouds
and all high energy phenomena. Recent advances in MHD turbulence call for
revisions in the paradigm of cosmic ray transport. We use the models of
magnetohydrodynamic turbulence that were tested in numerical simulation, in
which turbulence is injected at large scale and cascades to to small scales. We
shall address the issue of the transport of CRs, both parallel and
perpendicular to the magnetic field and show that the issue of cosmic ray
subdiffusion is only important for restricted cases when the ambient turbulence
is far from that suggested by numerical simulations. Moreover, on scales less
than injection scale of turbulence, CRs's transport becomes super-diffusive. We
also shall discuss the nonlinear growth of kinetic gyroresonance instability of
cosmic rays induced by large scale compressible turbulence. This gyroresonance
of cosmic rays on turbulence is demonstrated an important scattering mechanism
in addition to direct interaction with the compressible turbulence. The
feedback of the instability on large scale turbulence cannot be neglected, and
should be included in future simulations.Comment: 7 pages, 1 figure, submitted to ASTRONUM2011 conference proceedings,
typos correcte
Superdiffusion of Cosmic Rays: Implications for Cosmic Ray Acceleration
Diffusion of cosmic rays (CRs) is the key process of understanding their
propagation and acceleration. We employ the description of spatial separation
of magnetic field lines in MHD turbulence in Lazarian & Vishniac (1999) to
quantify the divergence of magnetic field on scales less than the injection
scale of turbulence and show this divergence induces superdiffusion of CR in
the direction perpendicular to the mean magnetic field. The perpendicular
displacement squared increases, not as distance along magnetic field, which
is the case for a regular diffusion, but as the for freely streaming
CRs. The dependence changes to for the CRs propagating diffusively
along magnetic field. In the latter case we show that it is important to
distinguish the perpendicular displacement in respect to the mean field and to
the local magnetic field. We consider how superdiffusion changes the
acceleration of CRs in shocks and show how it decreases efficiency of the CRs
acceleration in perpendicular shocks. We also demonstrate that in the case when
small-scale magnetic field is being generated in the pre-shock region, an
efficient acceleration can take place for the CRs streaming without collisions
along magnetic loops.Comment: 18 pages, 6 figures, erratum in eqs.(12,13) and table 1 included, ApJ
accepte
The Effects of Eicosapentaenoic Acid (EPA) and Docosahexaenoic Acid (DHA) on Brown Adipogenesis in Stem Cell Culture
Polyunsaturated fatty acids (PUFAs), especially eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are major maternal dietary supplements due to their positive benefits on neurological tissue growth during the first 12 weeks of gestation. Previous studies show that EPA and DHA inhibit muscle formation but promote adipogenesis. However, no research has addressed the question whether high intake of EPA and DHA affects brown fat development during gestation. The objective of this study was to measure the effect of EPA and DHA supplement on brown adipogenesis and potential pathways related to mitochondrial biosynthesis using fibroblasts as in vitro model. Using Oil-Red-O staining and PCR testing, lipid droplet formation and tested six genes were examined and PGC1α presented statistically significant difference from the control group when treated with PUFAs. Results indicated that PGC1α gene expression can be to be alternated by EPA and DHA treatment. Mitochondrial biosynthesis can potentially be promoted by increased PGC1α gene expression. However, the lipid droplets accumulated in the PUFAs treated group show an unknown mechanism of the n-3 PUFA on adipogenesis that needs to be revealed
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